Apparatus for cable splicing



March 21, 1950 R. J. VIQLETTE 2,500,969

APPARATUS FOR C ABLE SPLICING Filed Feb. 27, 1948 2 Sheets-Sheet lIIIII.

IIELEA IIELEB 1151.5?

28 25 29 I 26 Q/ H Q/ p 5 l a) March 21, 1950 R. J. VIOLETTE 2,500,969

APPARATUS FOR CABLE SPLICING Filed Feb. 27, 1948 2 Sheets-Sheet 2RICHARD J. VIOLETTE adv/wa Patented Mar. 21, 195% UNITED STATES (Grantedunder the act of March 3, 1883,. as.

amended April 30, 1928; 3'70 0. G. 757) 4 Claims.

This invention relates to the art of cable laying and more specificallyto joining and matching of cables for transmission of ultra-highfrequency power.

This application is a division of my copending application Serial Number545,533, filed July 18, 1944, now Patent No. 2,44!i,075.

It is an object of thisv invention to provide certain novel simpleapparatus for use in making cable splices.

Other objects of the invention will in part be obvious and in partappear hereinafter.

In the practice of this invention when cable of the coaxial type isjoined, the inner conductors of the segments are joined to be madeelectrically continuous and, following this, the dielectric, the outerconductor, and the outer jacket are re-formed to substantially themechanical and electrical equivalents of the original cable.

Formerly cables were commonly covered with rubber insulation ordielectric. Pressure of present day war conditions has necessitated thedevelopment of substitutes prominent among which are polyethylene andpolyvinyl chloride which in many respects are superior to rubber. Myinvention, set out in detail in the following paragraphs, is applicableto any thermoplastic resin sufiiciently workable to be formed into acable jacket or dielectric.

For a fuller understanding of the nature and objects of the inventionreference should be had to the following detailed description taken inconnection with. the accompanying drawings in which:

Figure 1 is a view in partial section of a dielectric gun used in thesplicing method of this invention;

Figure 2 in three parts, 2A, 2B, and, 2C, shows a sectional view ofconductors joined by means of. coupling units preparatory to forming thedielectric around the joints;

Figure 3A is a cross-sectional view of a mold for splicing cable;

Figure 3B is a cross-sectional view of the same mold in invertedrelation showing a joined cable therein preparatory to injection ofmolten dielectric into the joint;

Figure 4 is, an isometric view of a die used for forming a collar orflange on a cable;

Figure 5 is an isometric view of a die for making an impedance: matchingjoint to join a coaxial line of one characteristic impedance to one of adifierent characteristic impedance. This type of joint, is of vitalimportance in what is popularly called the impedance-matchingtransformer;

Figure 6 is an isometric view or a die used in making T junctions.

In the drawings there are shown only the most representative types ofdies that are used for making joints according to this invention.Actually right angle, straight-through, X, and Y joints can be made.with no substantial modification. of the apparatus used.

Referring to Figure 1, which is a diagram of a container for dielectric.material, the contents of which may be ejected in a manner likened to agrease gun. Said container willbe referred to as a dielectric gun, it isdesigned for use in this method of cable splicing, ll is the barrel ofthe gun having a threadedsection 12 on its, discharge end. Within thebarrel l2 of the gun is closefitting plunger l3 slidable up and down thebarrel. The plunger arm [4 passes through a head I5 forming the end ofthe gun. The handle It on.

the end of the gun may be of any convenient form.

The operation of the gun is evident from its design. Plunger I4, isdrawn back, the hollow barrel filled with extrudable or thermoplasticmaterial and the material extruded by working the plunger down. Whenusing the thermoplastic material, heat can be applied to the barrel ofthe gun by means of electrical heaters as is done with soldering irons,heating pliers, or by means of an openname. If it is desired to directthe extruded material into a die, the threaded end I2 of the gun can bemade to engage a corresponding fitting in the die. If the gun is notmade to size, an adapter ll, reducing or expanding, can be added to thegun.

- In Figure 2, are illustrated three common splices, which might have tobe made in a line, namely, a straight through connection 20, anexpansion or reduction 21 and, a T-junction 22. In each case illustratedthe joint is made by using a fitting like a plumbers coupling. Aconvenient form of coupling unit is one-threaded all the way throughwith threads of the same direction so that it can be used to joinconductors without having to twist the cables. The ends of theconductors to be joined are threaded back far enough to permit the endsof the conductors to abut when the fitting is put in place. The fl"-tings can be undercut as at 24, and 26, and provided with small holeslike 21, 28, and 29, to permit sweating the joint with a bit of solderfor the additional mechanical strength and efficiency of electricalcontact it would add. The conductors that can be joined thus may besolid, hollow or stranded. Also, for very small conductors or multiplestrand conductors the fitting can be unthreaded or dispensed withentirely and dependence placed on a twisted or braided joint.

In the figure, joint 2| is an illustration of the method of makingimpedance matching joints which, when completed leave no detectableelectrical hump in the line. Fitting 2| is made to the taper needed tojoin two conductors having different diameters or characteristicimpedances. The larger conductor 23 has its end threaded and hollowed asindicated. A smaller conductor can be fitted closely to the larger byway of the smaller opening in fitting 2! which may or may not bethreaded, and the joint sweated with solder.

A solid conductor shown as 23 can be joined to a multi stranded smallerone by means of fitting 2| by first passing the stranded conductor intoplace in fitting 2! through the smaller end bending back the strands toform a sort of knot in the larger section to keep the stranded conductorfrom pulling back through and finally joining the larger conductor tothe fitting and soldering the joint.

In Figures 3, 4, 5, and 6 there are shown isometric drawings of theapparatus and steps in the method used in finishing a splice. Figures 3Aand 3B show a die containing a pair of cable ends in which theconductors have been joined preparatory to the next step in the splicingoperation. The positional relations between Figures 3A and 38 as shownis such that Figure 3A may be rolled down upon Figure 3B to cover thecable joint and the entire mold will then be assembled. In the drawing3!) and 3! are the sections of coaxial cable being joined, 32 and 33 theouter jackets, 34 and 35 the outer conductors, 36 and 3': the dielectricseoarating the inner and outer conductors, and 38 and 39 the innerconductors. The inner conductors are shown joined by a coupling All likethat shown in Figure 2. The die is shown opened into two matchingsections comprising metal cores ll and heat insulating blocks 42. Ihedetails of construction of the die will be explained in conjunction withFigures 4, 5, and 6. A dielectric gun like that shown in Figure 1 isshown partially as 43.

In Figure l there is shown an isometric view of a die for use in moldingflange or peripheral ,collars onto cables in order to give stuiTingboxes a strong purchase in holding the cable in place. In this drawingthe halves of the die are separated to reveal its structure. The centralpart of the die 44 is usually a metal concave-shaped piece to form thecollar on the cable and is provided with a threaded reducing opening 45through which the dielectric material can be injected. To provide for agood match when the halves of the die are fitted together, pegs 46 aremade to match corresponding holes 41. The part of the die generallyindicated by 48 is made of a heat insulating material and its functionwill be explained in a subsequent paragraph. Insulating material 4 68can be transits, mikalex, asbestos, or silica brick.

Passage &5 is an air outlet passage to permit escape of air from the diewhen dielectric is injected into it.

In Figure 5 there is illustrated in isometric projection a die for usein splicing together cables of difierent diameters. In this figure, 58represents the metallic core of the die, which makes the transformationfrom one size to the other. Like the die illustrated in Figure 4, thisone is also fitted with a threaded reducing opening 5% through which thedielectric material can be injected. The heat insulating materialforming a substantial block on either side of the core of the die iindicated by 52. Pegs and matching holes for aligning the halves of thedie are designated as 53 and 54 respectively. A cable joint in which asmall conductor was joined to one more than twice its diameter is shownin place and designated 55. An air outlet passage is indicated as 56.

In Figure 6 there is shown in isometric projection a die for use inmaking T joints in cables. In the drawing, 60 represents the metalliccore of the die and 6! a threaded reducing opening for receiving adielectric injecting tool. The metal core of the die is backed up andinsulated at its ends by means of blocks of insulating material 63. Thetwo halves of the die are aligned by means of pegs 54 and matching holes65. An air outlet passage is indicated as 66.

The manner of making a splice with these dies can be readily understoodby reference to Figures 2 and 3. In Figure 2, one method of joiningskinned cables is shown. This rather elaborate operation involvingthreading the conductors is desirable when the conductor is about oneeighth inch in diameter or larger. With smaller sizes smaller unthreadedsleeves or lugs can be used or even carefully twisted joint. Anothergood method of connecting the cables is by brazing the ends together andthen filing the joint down to substantially the same diameter as therest of the conductor. If the joint is made with sleeves like thoseshown in Figure 2 the joint should be sweated with solder to perfect theelectrical connection.

After the conductors are joined they are laid in a die so that the metalcore of the die overlaps the dielectric surrounding the conductor asshown by parts 4!. 36 and 37 of Figure 3. In this way the conductor issecurely held concentric in the cable. The insulating portion of thedie, 42. grasps the dielectric beyond the exposed central conductor andholds it in alignment during the entire molding operation. Once theconductors are joined and the cable set in place, the halves of the dieare clamped securely around the cable by means of an ordinary C clamp;an injecting tool charged with dielectric material, shown as 43 inFigure is set into the feed hole of the die, the tool heated to makedielectric plastic and the dielectric forced into the die.

In constructing the dies it is necessary to provide a way for the air toescape from the die as the dielectric is forced into place. These airvents also serve as indicators in that the dielectric will appear whenthe die has received its full charge and are indicated in Figures 4, 5and 6 as 49, 56, and 66 respectively. It is essential that the joint befree of air bubbles for at high frequencies residual air causeselectrical humps in the line and at high voltages it can be the cause ofa breakdown.

dielectric in contact With it to flow. Were the l insulating blocks notprovided the die would become skewed on the cable and spoil the joint.

A coaxial .cable can be spliced by repeating the molding process. Thatis to say, firstthe inner conductors are joined; over the joint there isthen molded the dielectric after which the outer conductors are spliced;the final step involves placing the cable in a die made to fit theoutside diameter of the cable and molding over the spliced outerconductor a new outer jacket.

The same technique is applicable to the splicing of cable of differentsizes as shown in Figures 2 and 5. In Figure 2 there is shown a methodof joining the conductors of different sizes and in Figure 5 the dieused to form dielectric around the joint.

It is often desirable to pass a cable through a bulkhead in a mannersuch that the bulkhead will remain water-tight. This is accomplished bymolding onto the outer jacket a collar extending peripherally around thecable. The die for accomplishing this is shown in Figure 4. It isevident again in this case that successful molding of such a collarrequires that the cable remain concentric and in accomplishment of thepurpose the die is built with terminal insulators 48, to keep the moldfrom becoming skewed.

An improved stufiing box for receiving cable having molded thereoversuch a peripheral collar is described in the copending applicationSerial No. 545,532, filed July 18, 1944, now Patent No. 2,429,654, byRichard J. Violette and Irving H. Page.

The advantages of this invention can be summarized as follows:

Splices in cables can be made capable of withstanding voltages equal tothose for which the new cable is rated;

Splices in cable can be made so smooth and homogeneous that they willnot cause appreciable reflections in the line;

Cables of diiierent sizes can be joined for purposes of impedancematching without having the joint create any substantial electrical humpin the line;

In all the joints made by this method, the dielectric molded over thejoined conductors unites with the undisturbed dielectric to form aunitary continuous covering over the conductors;

The dies and accessories used are all small portable pieces and themaking of joints can be accomplished in the field by relativelyunskilled personnel;

The cores of the dies are small and of low thermal capacity and thusmake it unnecessary to heat the die in order to keep the dielectricplastic so it can flow into place;

The dies used are so constructed that they hold the cable concentric inthe die during the whole molding operation;

The dielectric trimmed away from the cable preparatory to making thejoint can be used to charge the gun or dielectric injection tool, andthus re-molded around the conductors to insure uniformity of compositionof the dielectric.

Although :certain specific embodiments of this invention :have beenherein disclosed and described, it is to be understood that they-aremerely illustrative of this invention, and modifications may, of course,be made without departing "from the spirit and scope of the invention asdefinedin the appended-claims.

The invention described herein may be manufactured and used by or forthe Government of the-United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

What is claimed is:

1. In :a system for making joints in coaxial cable transmission line, amold for joining the cable dielectric over said joint to avoid anelectrical discontinuity comprising, a pair of opposed hollow bodyportions for encompassing the cabl joint, said pair of opposed hollowbody portions being substantially symmetrical and adapted to be fittedtogether to form a mold cavity, said cavity having a shapecharacteristic of the cable joint, an intermediate portion of each ofsaid bodies formed of thermal conducting material, injection inlet meansand air outlet means communicating with said cavity through saidintermediate portion, and nd extremities odf each of said bodies formedof thermal insulating material, said end extremities being shaped tosnug- 1y grip the cable dielectric adjacent the joint with a minimum ofheat transfer.

2. In a system for making joints in coaxial cable transmission line, allllOld for joining the cable dielectric over said joint to avoid anelectrical discontinuity comprising, a pair of opposed hollow bodyportions for encompassing the cable joint, said pair of opposed hollowbody portions being substantially symmetrical and adapted to be fittedtogether to form a cylindrical mold cavity, said cavity having adiameter substantially equivalent to that of the cable dielectric, anintermediate portion of each of said bodies formed of thermal conductingmaterial, injection inlet means and air outlet means com.- municatingwith said cavity through said intermediate portion, and end extremitiesof each of said bodies formed of thermal insulating material to grip thecable dielectric adjacent the joint with a minimum of heat transfer.

3. In a system for making joints in coaxial cable transmission line, amold for joining the cable dielectric over said joint to avoid anelectrical discontinuity comprising, a pair of opposed hollow bodyportions for encompassing the cable joint, said pair of opposed hollowbody portions being substantially symmetrical and adapted to be fittedtogether to form a mold cavity, one end extremity of each body portionfoming a cavity portion shaped to snugly grip a cable dielectric havingone diameter, the other end extremity of each body portion forming acavity portion shaped to snugly grip a cable dielectric of anotherdiameter, all of said end extremities being formed of thermal insulatingmaterial to provide a minimum of heat transfer, an intermediate portionof each said bodies forming a cavit portion tapering from said onediameter to said other diameter, said intermediate portion being formedof thermal conducting material, and injection inlet and air outlet meanscommunicating with said tapered cavity portion through said intermediateportion.

4. In a system for making joints in coaxial cable transmission line, amold for joining the cable dielectric over said joint to avoid anelectrical discontinuity comprising, a pair of T- 'shaped opposed hollowbody portions for encompassing the cable joint, said pair of opposedhollow body portions being substantially symmetrical and adapted to befitted together to form a T-shaped mold cavity of cylindrical channelsthe diameter of the cable dielectric, an intermediate portion of each ofsaid bodies formed of thermal conducting material, injection inlet 10Number means and air outlet means communicating with said cavity throughsaid intermediate portion, and three end extremities of each of saidbodies formed of thermal insulating materialto grip 8 the cabledielectric adjacent the joint with a minimum of heat transfer.

RICHARD J. VIOLET'IE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Name Date 1,913,419 Watts June 13, 1933 2,174,377Bowden et a1 Sept. 26, 1939 2,287,163 Bishop June 23, 1942 2,361,348Dickson et a1. Oct. 24, 1944

